Where can I find statistics about the number of words children know at various ages?

I have checked the US Dept of Ed and the UNESCO homepage but have not been able to find info about vocabulary acquisition. Can anyone give me a lead?

Where can I find statistics about the number of words children know at various ages?
I couldn't find these figures, but here's some info on the subject; you could check the various books mentioned.


http://en.wikipedia.org/wiki/Language_ac...